Let d represent the amount of money Donavon brought to the fair.
After spending half his money on rides, he had half of it left: d/2.
After spending $3 on food, he had left (d/2 -3).
Donavon and his 3 friends together had 4 times this amount. They had $8.
... 4(d/2 -3) = 8
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The solution can be found by simplifying the equation, adding the opposite of the constant on the left, then dividing by the coefficient of d.
... 2d -12 = 8 . . . . . eliminate parentheses
... 2d = 20 . . . . . . . add 12
... d = 10 . . . . . . . . divide by 2
Donavon and each of his friends brought $10 to the fair.